CH662051A5 - NET TUBE-LIKE, FLEXIBLE, TRANSLUMINAL IMPLANTABLE PROSTHESIS. - Google Patents

Description

The invention relates to a mesh tube-like, flexible, transluminally implantable prosthesis made of stiff but flexible plastic or metal threads, which extends over the entire length of the prosthesis tube in the form of helical, intersecting turns around a common center line, which forms the longitudinal axis of the prosthesis, in such a way extend that an axial movement of the ends of the prosthesis causes a change in the diameter of the prosthesis tube.

The diameter of the prosthetic tube can be increased or decreased. Such a prosthesis is intended for arrangement within, for example, blood vessels of a living human or animal or for replacing a part of blood vessels or for arrangement in another location that is difficult to access. The prosthesis is particularly useful for mechanical transluminal implantation using an expandable self-attaching prosthesis for blood vessels, respiratory tract or the like. It can also be used to line the inner walls of damaged blood vessels or other organs with artificial tissue.

In surgery and other medical techniques, it is sometimes necessary to insert and expand a device, for example, in blood vessels, urinary tract, or other difficult-to-access places, the device having the function of supporting the vessel or pathway to position it there to be left.

The device according to the present invention can also be used in many medical applications, for example in different types of aneurysms which manifest themselves in a form of vasodilation, or on the contrary in stenoses which relate to contraction of blood vessels. The invention can therefore be used in particular to support or keep vessels of the venous system open, to close pathological vascular fractures, to bridge pathological vascular dilations or fractures in the inner walls of the vessels or to stabilize bronchial passages and bronchi. The device according to the invention can also be intended to act as a filter against thrombosis, for example by application in the inferior vena cava to prevent the formation of pulmonary embolism. The invention is particularly suitable for use as a prosthesis, for example as a graft, when used in blood vessels or other tubular organs in the body. However, it should be noted that the invention is not restricted to the applications mentioned, these are only to be regarded as examples.

In U.S. Patent No. 3 868 956 describes a device which can be expanded after insertion into, for example, a blood vessel. The active part of this device works on the basis of metal alloys which have a so-called «memory function», i.e. when the material is heated, it returns to its original shape. In this prior art, the heating of the material is accomplished by electrical heating with the device inserted at the point of interest. However, this technique suffers from the significant disadvantage that electrical resistance heating must take place in connection with surrounding sensitive tissues, which can be damaged during heating. It is stated in the patent specification (cf. column 3, lines 42-48) that the patient's blood acts as a coolant when the device is inserted into a blood vessel. However, blood is also a heat-sensitive material that can suffer undesirable coagulation when heated.

The present invention has for its object to provide a radially expandable and contractible prosthesis with which the disadvantages of the known techniques are avoided.

The present invention is based on the use of a prosthesis which comprises a flexible tubular body, the diameter of which can be changed by axially moving the ends of the body relative to one another. In a preferred embodiment, the body automatically assumes a radially expanded position when it is unloaded and free from external forces in the radial direction. The body

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consists of several individual stiff but flexible thread elements, each of which winds helically around the center line of the body as a common axis. A number of elements have the same winding direction, but are axially offset from one another. The stated number of elements of the same winding direction crosses a number of spring elements which are also axially offset from one another, but which have the opposite winding direction.

To obtain the desired function, the axially directed angle between the crossing elements is advantageously greater than about 600 and preferably obtuse, i.e. chosen greater than approximately 90 °. This state of the body refers to its state under radially unloaded conditions.

The crossing thread elements are preferably arranged in such a way that they form a type of wickerwork, which can be designed in any number of variants and can, for example, imitate certain known types of weave, for example according to the principle of simple weaving. The purpose of this measure is to give the tubular body the necessary stability. When n denotes the number of elements in the flexible tubular body, n preferably varies in the range from about 10 and more, for example up to about 50. The elements of the tubular body are preferably arranged symmetrically, i.e. the number of elements of each individual winding direction is in this context it should be noted that the reference to the number of elements in the tubular body is always to be understood as indicating those elements which are intended to maintain the supporting function of the body. The number n of elements is chosen according to the diameter of the body, the diameter of the element, the material of the element and other factors. In general, the larger the diameter of the body for a given material of the elements, the more elements are to be used to give the body the necessary stability.

The flexible, tubular body according to the invention was found suitable to be used as a prosthesis for transluminal implantation in blood vessels or other similar organs in a living body. The tubular body is contracted, i.e. with a reduced diameter used in the organism. After the tubular body according to the invention has been inserted, it is expanded and, according to self-fastening, it can remain in the expanded state at the point of use if the diameter of the body in the unloaded state is chosen to be somewhat larger than the diameter of the surrounding wall. This creates a certain permanent pressure on the inner wall, which ensures good fastening.

This implantation procedure is much simpler and less risky than the known implantation technique, in which a non-expandable prosthesis is used. The radially contracted prosthesis, which is inserted, for example, through the wall of the vessel at a certain distance from the implantation site, can be attached without requiring that the parts of the organ to be replaced be removed in a conventional manner. In this way, blood flow can be maintained even during an implantation, which has to be carried out in a short time. The prosthesis does not need to be sewn to the vessel and it is finally attached to the body after a few days thanks to the natural growth of the tissue, after a few months the growth of the tissue is complete and the inner wall of the prosthesis is covered with natural tissue.

The flexible tubular body can be expanded in various ways. It has been found that for many reasons it is advantageous to arrange the body in such a way that it automatically sets itself in the radially expanded and unloaded state. The expanded state can depend on the rigidity inherent in the thread elements, but it can also be controlled by elastic tendons, bands or membranes which are arranged in connection with the lateral surface of the body and extend axially along the same. Due to their elasticity, these tendons, ligaments or membranes cause an axial pull on the body in order to bring it into the expanded state.

Another possible way of imparting properties to the body that cause it to sit in a radially expanded position is to appropriately secure the elements together at their intersection, for example by some type of welding, gluing or the like.

The elements forming the flexible tubular body should be made of a medically acceptable material, such as plastic or metal, and should have some resilience or stiffness in combination with a suitable elasticity. The elements can consist of individual threads, for example of polypropylene, Dacron or other suitable plastic, or of a composite material. They can also be made from a suitable medically acceptable metal, such as. B. steel.

The free ends of the thread elements of the tubular body can be modified or protected in various ways. The variant, in which there are no free ends at all, consists in producing the tubular body as a whole from a coherent element. The next related variant is to connect the free ends formed on a body by cutting a long tendon with U-shaped links, which themselves in pairs at the ends of the elements in a suitable manner, e.g. B. are fixed by welding, gluing or the like. In this way, elements of the same winding direction or elements of opposite winding direction in pairs can be attached to one another.

Another embodiment is to weld the crossing points as a ring around the material by means of electrical resistance or the like before the tendon is cut, and then to cut at a point which is adjacent to and just outside the welding point. The ends then pointing outwards with respect to the welding point can be bent inwards in the direction of the interior of the body by means of slight plastic deformation, for example by controlled heating. Yet another design is to bend the free ends of the elements into loops.

As already explained, the tubular body according to the invention is suitable for use as a so-called graft. In this case, the body can act as a graft, especially if it is made from elements with properties that inherently give it the desired density and porosity, so that the body can act as a graft, with at least a certain number of elements made of multiple threads Materials or the like can be produced. As an alternative to the elements themselves giving the body the desired density, a certain type of surface layer is applied to the body, for example from

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Plastic or other suitable material. By attaching such a surface layer, the crossing points can be fixed at the same time as indicated above, so that the body tends to take an expanded position.

A separate sleeve or membrane can also be arranged outside or inside or combined with the body. This can consist of a stocking made of porous tissue, which encloses the body and can be implanted at the same time. In this case, the stocking can be adaptable to the body in connection with its expansion, either by the stretchability of the fabric or by overlapping folding or in another way, for example by manufacturing according to the same principle as the body from a plurality of thread elements. It is also possible to think of using a knitwear-like product or crimped yarn textiles. When using such a separate member, it is preferably fastened in the axial direction relative to the body so that it is finally in the correct position when it is inserted into a large vessel or the like.

The expansion or contraction of the tubular body can take place with the aid of a device provided with means for stretching or shortening the body. Such means can be designed in various ways, for example in such a way that their design enables the ends of the body to move axially relative to one another in order to reduce or enlarge the diameter of the body. The device should include gripping members capable of gripping the ends of the body and moving them towards each other. The gripping members should be arranged so that they can be released at the desired location after insertion of the body so that the device can be removed from the location in question except for the body. In an alternative, the device comprises a flexible tube, into which the tubular body is to be put in the contracted state, and functional members, with which the body can be ejected from the tube while being expanded, in order to be placed in the desired position.

Other characteristic features emerge from the patent claims.

The invention is described below on the basis of non-restrictive but exemplary embodiments with reference to the drawing. These training courses are illustrated in the drawing and show:

1A and 1B show a schematic side and end view of a flexible, tubular body according to the invention;

Figures 2A and 2B show the same tubular body as in Figure 1, but in a contracted condition;

3 and 4 a separate thread element of the body, the body being shown in the contracted or expanded state;

Figure 5 is a schematic construction comprising the tubular body according to the invention;

6 shows an enlargement of part of FIG. 5;

7 shows an alternative embodiment of the tubular body;

8 shows a tubular body designed as a combined graft and filter;

9 shows the tubular body in an application as a graft in connection with an aneurysm;

10 shows a diagram of the diameter (D) of the body as a function of the angle and the elongation of the prosthesis in percent; and

11 shows a schematically represented alternative of a construction for manipulating the prosthesis according to the invention.

1A and 1B show an example of a prosthesis in the form of a cylindrical tubular body, generally designated 1. 1A, the outer surface of the body 1 is formed from a number of individual thread elements 2, 3 etc. and 2a, 3a etc. From these elements, the elements 2, 3, etc. extend helically and axially offset from one another, with the center line 7 of the body 1 as a common axis. The other elements 2a, 3a, etc. extend helically in the opposite direction, the elements extending in the two directions crossing each other in the manner shown in Fig. 1A.

The diameter of the tubular body formed in this way can be varied if the ends of the body are axially offset from one another in the direction of the center line 7. FIG. 2A shows how the tubular body 1 according to FIG. 1A has a smaller diameter in that the ends 8, 9 are separated from one another in the direction of the arrows. Fig. 1B shows the diameter of the tubular body in an expanded state, while Fig. 2B shows the diameter of the body 1 in a contracted state after its ends have been removed 8,9 from each other.

3 and 4 show a detail taken from FIGS. 1 and 2, in particular a single thread element of the tubular body 1 and the manner in which its helical shape changes in connection with the change in the length of the tubular body 1.

FIG. 3 shows the individual element 10 which corresponds to element 10 in FIG. 2A. The diameter of the turn is equal to di and the length of the element is equal to 11. In FIG. 4 the same element 10 is shown after the tubular body has been expanded to the state shown in FIG. 1A. The diameter of the turn was now larger and is called d2, while the length became smaller and is called 1t.

The tubular body 1 can be expanded in various ways. As mentioned above, the body preferably has the property of assuming an expanded position by itself in the unloaded state. In the present description, the term "expanded position" always refers to a radial expansion, i.e. to a condition with a larger diameter of the body 1. The property of expanding by itself can be created by providing the body with tendons or ligaments that extend in the axial direction and parallel to the lateral surface of the body. An example of such an embodiment is shown in FIG. 7, in which the tubular body 1 is provided with axial chords or bands 11. These tendons or ligaments 11 are suitably shown made of elastic material and suitably fastened to the elements of the tubular body 1 when the body is in the expanded state. If the tubular body 1 is now stretched in the axial direction by removing its two ends from one another, the elastic tendons or ligaments 11 are tensioned. When the tension ceases to act on the body 1, the elastic tendons or ligaments 11 compress the body 1 in the axial direction, with the result of a corresponding increase in the diameter of the body.

The tubular body 1 can be provided with the same tendency to assume the expanded position by the elements 2, 3, etc; 2a, 3a etc. at the crossing points 5, 6 (Fig. 1), as mentioned earlier, are attached. Another way to create this effect is

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in providing an inner or outer tubular elastic member, for example made of a thin elastomer, which is attached at least to both ends of the tubular body.

In Fig. 5, a device, generally designated 18, is shown, which enables the tubular body 20 to be pulled into the desired position, e.g. a blood vessel. The tubular body 20 comprises the front tubular part 19 of the device 18 and is attached to gripping means 21 and 22 at both ends thereof. The front tubular part 19 of the device is connected to an active member 24 by means of a flexible tubular means 23. The gripping means 21 and 22 can be controlled in the desired manner with the aid of active elements 25, 26 and 27 of the active member 24.

FIG. 5 shows schematically how the device 18 with the contracted tubular body 20 was inserted into, for example, a blood vessel, this being shown in the drawing with dashed lines and designated by 28. The active member 24 is connected to the gripping means 22 in such a way that when the active element 26 is moved forward into the position 29 shown with dash-dotted lines, the gripping means 22 is brought into the position 30 shown with dash-dotted lines in a corresponding manner. As a result, the end of tubular body 20 has been moved from layer 22 to layer 30, while in the present case the other end of the body remains in layer 21. At the same time, the diameter of the body 20 has increased and the body 20 has expanded when the end thereof has reached the layer 30, i.e. the body has been brought into contact with the inner wall of the vessel and has assumed the position 31 shown with a dash-dotted line. Since both ends of the tubular body 20 are still held by the gripping means 21, 22, the body 20 assumes a balloon-like shape in its expanded state.

The active element 27 is also connected to the gripping means 22 by a part, for example by a wire which is guided in the tubular means 23. In this way, the gripping means 22 in its position 30 can be actuated by axial movement of the active element 27 in order to release the end of the body 20. In the same way, the active element 25, which is connected to the gripping means 21, can detach the front end of the tubular body from the gripping means 21 by axial movement. The ends of the elastic body 20 are thereby moved directly to each other to effect expansion, and the prosthesis assumes its expanded shape inside the blood vessel.

6, the construction of the front tubular part 19 of the device 18 is shown in more detail. The tubular body 20 has two ends 32 and 33 and includes a thin-walled flexible tube 34 that runs within and concentrically with an outer flexible tube 35, the two tubes forming the flexible tubular means 23 of FIG. 5. At the front part of the inner tube 34, an annular member 36 is arranged, in which the end 32 of the tube 20 is inserted. In a corresponding manner, the end 33 of the tube 20 is inserted into an annular member 37 which can be moved in the axial direction with respect to the tube 34 surrounded by the ring 37. An inner gripping means or gripper 38 is provided on the front part of the tube 34. The gripper 38 is suitably made of spring steel and has a front pointed part 39 which is bent approximately at right angles. This part 39 extends radially outwards through a hole in the wall of the tube 34. It can be moved in the radial direction by the action of a ring 40 which is axially movable and is arranged inside the tube 34. The ring 30 is connected to a wire rope 41, by means of the axial movement of which the gripper 38 can be moved in the radial direction. In Fig. 6 the gripper 38 is shown in such a position that its pointed part 39 has pierced the end 32 of the body 20 and thereby holds the said end in place.

In a corresponding manner, another gripper 42 is provided in order to hold the end 33 of the tubular body 20 from the outside by means of its pointed part 43. This gripper 42 is fastened to the outside of the tube 35 and can be moved in the radial direction by means of a ring 44 which is arranged around the tube 35 and is fastened to a wire rope 45 which extends between the tubes 34 and 35. The wire cables 44 and 45 are connected to the respective active elements 25 and 27 of FIG. 5.

If the attached and axially elongated tubular body 20 is to be detached from the remainder of the device after the body has been radially expanded, this is accomplished by releasing the pointed parts 39, 43 of the respective grippers 38 and 42 from the ends of the tubular body 20 by actuating the rings 40 and 44 by means of the active elements 25 and 27 via the wire cables 41 and 45 in such a way that the grippers 38 and 42 are deflected. The ends 32 and 33 of the body 20 are then released by axial displacement of the tubular part 19 of the device. As can be seen from FIG. 6, the front end of the device is protected by a hood or casing 46 attached to the ring 36.

As mentioned above, the expanded tubular body has various applications in surgery. The design shown in FIG. 1 can be used, for example, to support the walls of the vessels. 8 shows a modified design of the flexible tubular body. In this embodiment, the body consists of a circular cylindrical part 53, which at one end deforms to a taper or to an end part 54, which also consists of thread elements. This device has been found suitable for use as a sieve or filter to prevent thrombosis. The device according to FIG. 8 can be used at a desired location in a blood vessel, for example in the inferior vena cava, with the purpose of preventing pulmonary embolism. Known filters for insertion into blood vessels against thrombosis have the disadvantage that they are finally fixed in the blood vessel by pointed ends or clamps or the like, it being impossible to correct the position or remove the filter. An example of such a device is shown in U.S. U.S. Patent No. 3,540,413. The device according to the invention can be inserted into the vena cava with great precision and does not entail the risk of damage to the surrounding vessel walls, which is the case with the known devices which are currently used for the same purposes in surgery.

FIG. 9 shows a tubular body according to the invention which is intended for use as a graft. In this case, the body 55 has a much denser wall than in the embodiments according to FIGS. 1 and 2. This denser wall can be achieved by inserting an elastic yarn between the supporting thread elements 2, 3, etc .; 2a, 3a, etc. of FIG. 1 can be produced. In this way, a wall of predetermined porosity can be formed. This tubular body with a more or less porous wall is therefore a kind of expandable graft and it has many uses.

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In the application shown in FIG. 9, the body 55 is inserted in an aorta 56 which has an aneurysm 57 in the form of an expansion of the vessel wall. Given that the expandable body or graft 55 can be inserted some distance from the damaged area of the aorta and only then positioned in the center of the aneurysm, it is bridged and does not need to be surgically removed. 9 also shows that the aorta is a conical blood vessel. In this case, the procedure will therefore be such that the prosthesis is inserted in the form of a graft with an instrument which is designed, for example, according to FIG. 5. After the graft or body 55 is inserted, it is expanded. Given the conical shape of the aorta, the following surgical technique is used.

The front end 32 of the graft 55 of FIG. 5 is inserted a little further into the aorta than the location where it should be after the operation is complete. This position 59 is indicated in FIG. 9 with a dash-dotted line. The other end 22 of the axially elongated graft 55 according to FIG. 5 is brought into the end position corresponding to position 60 in FIG. 9 before the radial expansion is carried out. Since this part of the aorta has a slightly smaller diameter than the diameter at an upstream location, the prosthesis cannot expand more than the diameter at the end

60 corresponding dimension. This is remedied, however, by the other end of the graft 55 then being moved from the position 59 to the position 58 by means of the front part of the instrument, so that this end of the graft can expand sufficiently to connect with this point of the vessel wall .

11 shows another embodiment of the device for expanding the tubular body.

This device forms a flexible instrument for inserting the tubular body in a contracted state, for example into a blood vessel, and for subsequently expanding the body when it is positioned therein. The parts of the instrument are an outer flexible tube 61 and a concentric, also flexible inner tube 62. An active element 63 is arranged at one end of the outer tube. Another active element 64 is attached to the free end of the inner tube 62. In this way the inner tube 62 is in relation to the outer tube

61 axially displaceable. At the other end of the inner tube

62, a piston 65 is fastened which, as it moves, runs along the inner wall of the outer tube 61.

To use the instrument, the tubular expandable body 69 is first inserted into the tube 61 in the contracted state, the inner tube 62 with the piston 65 being inserted in the rear part 66 of the outer tube 61. The starting position of the piston 65 is shown by dashed lines at point 67 in FIG. 11. In this way, part of the tube 61 is filled with the contracted tubular body 69 in the starting position.

During insertion, the flexible tubular part of the device is brought to the location of the blood vessel that was intended for insertion. The active element 64 is then moved in the direction of the arrow 68, the contracted body 69 being expelled through the end 70 of the tube 61 and the part of the tubular body 69 which leaves the end 70 of the tube expanding until it expands in it Layer 71 contacts the inside of the wall 72 of the vessel. The tubular body 69, 71 is shown in FIG. 11 for simplicity by two sinusoidal lines. To the same extent

As the expanded body 71 communicates with the vessel wall 72, the end 70 of the tube is displaced in the direction of the arrow 73 by movement of the active element 63. The contracted body 69 is moved by the piston 65 which presses against one end of the body. As a result, the insertion takes place by means of simultaneous opposite movements of the active elements 64 and 63, the movement of the active element 64 being greater than the movement of the active element 63. When the contracted body 69 has been completely pulled out of the tube 61, the expansion is complete and the instrument can be removed from the surgical site.

The embodiment according to FIG. 11 has the great advantage that the details of the construction are very simple and work with high reliability. The instrument shown is also suitable for the insertion of helical objects of very small diameter. As an example, it can be mentioned that tests were carried out with a tubular expandable body consisting of crossing thread elements, the diameter of the body being only 2 mm in the contracted state and 6 mm in the expanded state. It is also quite conceivable to use bodies with an even smaller diameter. The instrument according to FIG. 11 can advantageously also be used for the insertion of bodies in the form of grafts of very large diameters.

When inserting longer bodies, it is conceivable that the resistance of the same to the displacement in the tube 61 becomes too high. In this case, it may be appropriate to replace the piston 65 at the front end of the tube 62 with movable claws or grippers that function in such a way that when the tube 62 is brought forward in the direction of arrow 68, the grippers Grasp the inside of the body 69, which moves the body forward. When the pipe 62 is returned in the direction of arrow 73, the grippers are released. In this way, the body 69 can be moved forward by pump-like movement of the tube 62.

Of course, several configurations of the different parts shown in FIG. 11 are conceivable. So it is e.g. possible to simplify the insertion for the surgeon by mechanically controlling the relative movement of the active elements 63 and 64 to one another.

It is important that the expandable body has certain elastic properties in order to be used successfully. For example, when the body is used to keep blood vessels open or to act as a blood vessel prosthesis, the body should have elastic properties that are largely similar to those of the blood vessels of the living body. The body must also be immovable in relation to the blood vessel while it is exposed to stress and deformation. The body must be resilient in the radial and axial directions at the same time in order to have sufficient adaptability so that it can follow the pulse of the blood or the flexion of a limb. The body should also have an inherent stiffness to maintain its shape, for example, against external pressure, and it should be strong enough to withstand internal pressures.

In order to achieve these properties, it is desirable to carefully choose materials and dimensions of the thread elements of the body and to adapt them to the actual area of application. In addition to the obvious requirement that the material of the thread elements be compatible with the fabric, i.e. among other things, that it causes a minimal rejection reaction, is not toxic and that

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Allowing cell growth, it can generally be said that the material should be stiff and elastic and should not be plastically deformable to any appreciable extent. The material can consist, for example, of individual threads of polyesters, polyurethanes, polycarbonates, polysulfides, polypropylene, polyethylene, polysulfonates, stainless steel or silver. The diameter of the individual threads should preferably be in the range from 0.01 to 0.5 mm.

It has been found that in certain cases it is important that the angle α between the thread elements of the body, for example between 2 and 2a of Fig. 1A, is sufficiently large when the body is expanded or in an unloaded or almost unloaded state , among other things, to meet the above conditions. It was found that the larger the angle a, the higher the stability of the body against external pressure. From this point of view the ideal would be an angle of 180 which is practically impossible. The angle shown in Figure 1A is around 160 which is normally close to the upper limit.

In order to change the diameter of the body, it is necessary that, as indicated, the two ends of the body are axially displaced from one another. 10 shows the general characteristic of this movement. The percentage change in diameter when the ends are separated from each other was shown along the ordinate, along the abscissa the corresponding percentage change in length was shown as extension. Along the abscissa, the angle a was also shown as a function of the diameter of the body.

As can be seen from Fig. 10, at the beginning of the stretching, the relative reduction in diameter is small, and the diameter is reduced by the order of 90% when the stretching is 100%, based on a starting position where the angle oc is as close to 180c as is practically achievable. With a stretch of 200%, the reduction in diameter is 75% corresponding to an angle a of 100 °. The reduction in diameter accelerates with increasing stretch. For example, increasing the aspect ratio from 250 to 300% means reducing the diameter from 60% to 30%, i.e. there is a relatively large reduction in diameter with a relatively small stretch. In this area, the angle is reduced from approximately 700 to 40 °. As indicated above, in certain cases it is desirable that the expanded body take a position that is as far as possible on the left side of the characteristic of Fig. 10, i.e. the angle a should be as large as possible. Since the body used is to come into contact with the wall of the vessel with a certain pressure in order to remain attached, the diameter when inserting it must be smaller than the diameter during free expansion.

If expandable bodies according to the invention are used for insertion into blood vessels or other tubular organs, the forces required for expansion can be exerted, for example, by elastic means, such as elongate elastic tendons, which are attached to the crossing point of the thread elements of the helical arrangement. By choosing a large angle a, when the elastic means are attached to the elements, the conditions mentioned above are easily met.

The reason that a large value of the angle a is often desired is that the elastic properties of the prosthesis deteriorate as the angle decreases. For example, under external radial pressure, the resistance to deformation is small and there is a risk of local axial displacement between the prosthesis and the wall of the vessel, which can hinder cell growth at the location of the displacement. Another reason to choose a large value of the angle a is when a high expansion ratio is desired, i.e. with a large ratio between the diameter of the expanded body and its diameter when contracted. For example, to obtain an expansion ratio of more than 2 up to about 3, the angle a should be more than about 120. The choice of the angle a also depends on the material of the thread elements of the prosthesis. When choosing a plastic material, too small an angle a results in too high a suspension in the radial direction. In certain cases, however, it may be desirable to choose a smaller angle a, particularly in those cases where significant radial yielding is desired.

Another case in which a high value of the angle a may be desired arises in the applications where the prosthesis used will be subjected to bending stresses. The resistance of the prosthesis to flattening will be all the greater as the angle a is larger. Therefore, it is desirable to choose an angle a greater than about 60: an obtuse angle could be particularly suitable. In order to ensure a high resistance to external pressure or to achieve high expansion ratios, it is advantageous to choose an angle a of at least approximately 120 °.

From Fig. 10 it can be seen that the body has to be strongly stretched when large angles a are used. For transluminal implantation through openings of small diameter, the extension, starting from large angles a, can be considerable and can be up to 300% and more.

For example, if vascular prostheses or similar devices are used, e.g. In order to keep blood vessels open, it is generally desirable to exert a pressure against the immediate vessel wall that is at least 133 mb. There is also a maximum pressure that must not be exceeded. This maximum pressure changes from case to case, but may not exceed about 666 to 1333 mb when used as a vascular prosthesis. If the desired pressure is achieved by elongate elastic members or by an elastic sleeve or membrane, the necessary fastening pressure can be caused by forces of reasonable value if a large angle a is chosen, which is therefore advantageous. Calculations show that with regular cylindrical contact between the vascular prosthesis and the surrounding vessel wall, a total force of a few Newtons (approx. 0.1 to 0.2 kp) is required to achieve an attachment if the angle a 150 to 170? is. This fact also helps to avoid the risk of an adjustment of the inserted prosthesis by external forces, since the resulting frictional forces are sufficient to avoid such an adjustment. For example, if the angle a is 45: a force of approximately 10 to 20 Newtons (1 to 2 kp) is required, which is disadvantageous in practice.

In order to make the prosthesis according to the invention function satisfactorily, inter alia in order to give it the necessary fastening in the inserted state, such conditions must be met with regard to the elastic material that the necessary expansion force results from this. The material must also have acceptable adhesiveness to the thread elements of the body and, of course, must be biologically acceptable for the implantation. Therefore, the material should have a low modulus of elasticity and a linear relationship between the

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Force and stretch, at least up to a stretch of 250 to 600%, and it must not have any significant hysteresis.

There are elastomer groups which meet the above conditions and have been found suitable for use in the production of expandable bodies according to the invention. Such elastomers are included in the group of materials known as segmented polyurethanes (PUR), some of which are commercially available under trade names such as PELETHANE (UpJohn), BIOMER (Ethi-con), ESTANE (Goodrich). These materials can be dissolved in suitable solvents to create solutions from which thin elastic bands or thin-walled tubes can be made to attach to the supporting thread elements of the helical arrangement that forms the framework of the body.

If the prosthesis according to the invention is used as a so-called graft or vascular prosthesis, the wall of the prosthesis, as already mentioned, should be porous, thin and compatible with the tissue and its composition should allow the growth of natural tissue and the like. a. from Neointima. Segmented polyurethanes (PUR) are also suitable for producing such walls, since the properties mentioned can be combined with the requirement for a wall with a very high elasticity. Such walls can be produced in the form of a thin tube, which consists of fibers from segmented PUR, which are formed by extrusion from a solution of PUR. The fibers are connected to one another at their crossing points and the wall can be produced with the desired porosity by suitable adaptation of, for example, the thickness and the density. The resulting tube can surround the body or it can be fastened inside. Optionally, the thread elements of the body can be combined with the material of the tube, in a suitable manner in the manufacture of the tube.

In order to give a vascular prosthesis the desired expansion force, straps made of PUR can be combined with a suitable porous wall material, which can consist of monofibers or multiple fibers woven between the thread elements of the body or of a porous, elastic wall produced as described above.

In certain cases, it may be suitable to manufacture the body or its bands, sleeve or membrane from a biodegradable material, for example from polyamide and / or polyurethane.

The following are non-limiting examples of training courses in which the inventive idea has been applied.

Example 1 Vascular Implant Expanded Diameter 20 mm Angle a 160 '

Length 100 mm

Suitable for insertion into the aorta in the diameter range from 15 to 18 mm

Smallest diameter before insertion 8 mm total extension about 300%

Calculated axial fastening force 1 N (0.1 kp) caused by a microporous elastic wall made of PUR with a pore size of 15 to 50 µm and a thickness of 0.15 mm

Material of the thread elements: polyester monofiber with a diameter of 0.15 mm number of elements n = 72 (2 x 36).

Example 2 Vascular prosthesis against stenosis Expanded diameter 6 mm angle a 1000 length 200 mm

Use in veins in the diameter range from 4 to 5 mm. Total extension 250%

Axial expansion force 0.8 N (0.08 kp) caused by four elastic bands made of segmented PUR, each with a width of 1.5 mm and a thickness of 0.4 mm. Material of the thread elements: polypropylene monofiber with a diameter of 0. 09 mm and a number of elements n = 36 (2 x 18).

Two or more tubular bodies can be arranged concentrically one above the other in order to give the body stability. This is particularly useful when thread elements with a small diameter are used and / or when the number of elements is small.

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Claims (12)

662 051 2nd PATENT CLAIMS 1. Net tube-like, flexible, transluminally implantable prosthesis (1) made of stiff but flexible plastic or metal thread (2,3, ... etc.; 2a, 3a, .. etc.) that extends over the entire length of the prosthesis tube (53) extend in the form of helical, intersecting turns around a common center line (7), which forms the longitudinal axis of the prosthesis, such that an axial movement of the ends of the prosthesis causes a change in the diameter of the prosthesis tube. 2. A prosthesis according to claim 1, in which the axially directed angle (a) between the plastic or metal threads (2,3, .. etc.; 2a, 3a, .. etc.) of the crossing turns is greater than about 60 ° and is preferably blunt. 3. Prosthesis according to one of claims 1 or 2, in which the intersecting turns are arranged like a wickerwork to give the prosthesis (1) stability. 4. A prosthesis according to one of claims 1 to 3, in which the number of plastic or metal threads (2, 3, .. etc.; 2a. 3a ... etc.) of the intersecting turns is approximately equal to 10. 5. Prosthesis according to claim 4, in which the number of plastic or metal threads of one winding direction (2,3, .. etc.) and the other winding direction (2a, 3a, .. etc.) is approximately equal to each other. 6. Prosthesis according to one of claims 1 to 5, in which to achieve the radially expanded state of the prosthesis tube elastic members such as tapes (11) are provided, which extend axially along the lateral surface of the prosthesis tube and pressurize it axially. 7. A prosthesis according to any one of claims 1 to 5, in which an elastic and preferably porous membrane is provided to achieve its radially expanded state of the prosthesis tube, which extends along the lateral surface of the prosthesis tube and puts this axially under pressure. 8. The prosthesis of claim 7, in which the membrane extends substantially the entire length of the prosthesis tube. 9. Prosthesis according to one of claims 6 to 8, in which the limbs or the membrane consists of a preferably porous, segmented polyurethane-containing material. 10. A prosthesis according to any one of claims 1 to 5, in which the plastic or metal threads are attached to one another at their crossing points (5, 6) in order to automatically bring the prosthesis tube into its radially expanded state. 11. A prosthesis according to any one of claims 1 to 10, in which the prosthesis tube (53) is formed at least at one end (54) with a tapering diameter in order to act as a filter after insertion. 12. Prosthesis according to one of claims 1 to 11 in the form of a graft for vessels.